1. Field of the Invention
The present invention relates to the field of displaying information on a visual device. More specifically, the present invention relates to an apparatus for reducing the display intensity of a screen of a cathode ray tube.
2. Prior Art
In a typical display screen utilizing a cathode ray tube (CRT) to provide a visual display, an unchanging image on the screen will tend to burn that image into the CRT. The video image which results from a high-intensity beam striking the back face of the CRT screen cause the presentation of images on the front of the screen. However, when this high-intensity beam continues to provide an unchanging pattern on the screen for a prolonged period of time, the particular image is permantly "burned-in" on the screen. The burned-in image is quite noticeable even when the CRT is completely deactivated. Normally, this problem results when a video terminal is left unattended for a prolonged period of time, wherein a video pattern is unchanging during this unattended period.
To prevent this burn-in of the CRT, various "screen saver" functions have been implemented in video terminals in the prior art. A typical screen saver funtion implements a circuit for monitoring an interactive device, such as a keyboard. If no interaction has occured for a given period of time, the circuit interacts with the contrast control of the CRT and blanks the screen. Although the blanking function removes high-intensity video images from the CRT, it also leaves the video screen blank. Leaving the screen in the blank mode is disadvantageous because it is difficult to tell if the screen is on or off. Instead of proceeding to a blanking mode, another prior art method never permits the pattern to remain constant once the screen saver function is activated. In this instance colors are changed every few seconds, or a pattern is made to float across the screen randomly preventing any stationary image to remain on the screen.
It is appreciated then, that what is needed is a screen saver function which provides a continuous and unchanging video pattern which will not burn-in the CRT screen.